Semiconductor component with a high breakdown voltage

ABSTRACT

The invention relates to a semiconductor component with a base zone ( 3 ) extending in a lateral direction (x) of a first type of conductivity (n) and at least two contact areas ( 1, 2 ) for connection to electric contacts (A, K) which zones are separate at least from the base zone ( 3 ) in the lateral direction (x). A base material of the base zone ( 3 ) is silicon (Si) and has a dopant concentration of 10 12  to 5×10 14  cm −3  and a respective dopant concentration (N A ) along a lateral direction (x) of less than 2×10 12  cm −2  determined by integrating the dopant concentration across the vertical thickness of the base area ( 3 ). The semiconductor component further comprises compensation layers ( 6, 6   a   , 6   b   , 6   c   , 7, 7   a   , 7   b   , 7   c   , 8 ) of a second type of conductivity (p) opposed to the first type of conductivity. Said layers extend inside or outside the base area in a lateral direction (x).

The invention relates to a semiconductor component with a low-doped baseregion of the first conductivity type extending in the lateral direction(x) and two terminal areas which are separated at least by the baseregion in the lateral direction for connection to electrical contacts.

These semiconductor components are used especially in power electronicsto accommodate blocking voltages in the high voltage range, i.e., the kVrange. Here the low-doped base which is made especially as a n⁻-base isused to accommodate blocking voltages. The high voltage on the contactsis distributed accordingly over the entire semiconductor component, thevariation of the high electrical field strength being adjusted in thebase region. Since the voltage is an integral of the electrical fieldstrength over the lateral direction and the allowable field strength inthe semiconductor material, generally silicon, is limited by thepertinent breakdown field strength, these components are produced with agreat lateral extension of the base region.

To achieve breakdown voltages as high as possible, a slope of theelectrical field-strength distribution which is as small as possible andthus doping of the base region as low as possible are necessary. Theallowable maximum base doping drops with increasing breakdown voltage.With respect to the required cosmic radiation resistance of thecomponents they must be dimensioned such that the maximum attainedelectrical field strength is clearly below the breakdown field strengthof the semiconductor material used, by which the essentially attainableblocking voltage is further reduced.

A further reduction of the blocking voltage which can be accomplishedwith a stipulated doping arises in so-called punch-through dimensioningfor improving the on-state behavior, for which the base width of thecomponents is chosen such that the electrical field at higher blockingvoltages extends as far as the cathode emitter. An increase of theallowable blocking voltage is thus only possible by using semiconductormaterial with lower doping than the commercial starting material, butone such lower-doped semiconductor material cannot be economicallyproduced.

Thus, when using commercial starting material, for example silicon withminimum doping of roughly 5×10¹² cm⁻³, components with breakdownvoltages up to roughly 10 kV can be produced. Higher blocking voltagescan only be accomplished by series connection of several components, forexample stacked diodes. Since in the conducting state for each of theseries connected components at least the diffusion voltage is necessary,these components have poor on-state behavior with a correspondingly highvoltage drop.

DE 43 09 764 C2 shows a component with a base consisting of several thinsuccessive layers which are alternately p-doped or n-doped. The dopantcontent in each individual layer is quantitatively the same and is solow that they are completely cleared at very low blocking voltages. Forthis purpose complex formation of successive layers of very lowthickness with relatively high doping is accordingly necessary so thatproduction is complex and expensive.

DE 196 04 043 A1 shows a semiconductor component which can be controlledby a field effect, with a drain zone of the first conductivity type, agate electrode which is insulated relative to the drain zone, and asource region of the second conductivity type, made in the drain zone.In the drain zone, areas of the first and second conductivity type areformed, the concentration of the added n-regions corresponding roughlyto the concentration of added p-regions. EP 0 818 825 A1 shows athyristor in which the anode regions are separated from he cathoderegion among others by a doped substrate region. On the outer edge ofthe substrate area layers are formed which are of one conductivity typewhich is opposite the conductivity type of the substrate area.

The latter two publications are however not suited for high voltageapplications as a result of their structure.

The object of the invention is to be able to produce a semiconductorcomponent easily and economically and to enable use at high blockingvoltages.

This object is achieved by the base material of the base region (3)being silicon (Si) and the dopant concentration of 10¹² to 5×10¹⁴ cm⁻³and the dopant concentration (N_(A)) determined by integration of thedopant concentration over the vertical thickness of the base region (3)along the lateral direction (x) being each less than 2×10¹² cm⁻², bythere being compensation layers (6, 6 a, 6 b, 6 c, 7, 7 a, 7 b, 7 c, 8)of the second conductivity type (p) opposite the first conductivity typewhich extend inside or outside the base region in the lateral direction(x), the lateral length (l_(K)) of the compensation layers being greaterthan their vertical thickness (d₆, d₇) and the dopant surfaceconcentration (N_(A)) which is determined by integration of the dopantconcentration over the vertical thickness of a compensation layer alongthe lateral direction (x) being less than 1×10¹² cm^(−2.)

The compensation layers can run on the outside of the base region oralso within the base region. Here it is fundamentally also possible forthe compensation layers to extend not only in the lateral direction, butalso roughly in the vertical direction in their variation.

The invention is based on the idea of at least partially compensatingfor the space charge in the base region by layers of opposite dopingwhich run essentially parallel thereto. Here individual sections can bemade along the lateral direction, in which this compensation turns outto be of a different magnitude, and in part also complete compensationcan be achieved, or overcompensation in which upon integration over thevertical thickness there is a higher dopant content of the compensationlayers. Advantageously, in the compensation layers the dopantconcentration is less than that breakdown dopant concentration whichcorresponds to the breakdown field strength of he correspondingsemiconductor material. The semiconductor material can be especially thesilicon which is conventional for power semiconductor components withdoping of 10¹²-10¹³, especially 3×10¹²⁻10¹³. Thus, semiconductorcomponents for applications preferably in the range 10-30 kV can beformed.

The terminal regions can consist especially of a highly dopedsemiconductor material.

The terminal regions can be especially an anode region of p⁺-conductivesemiconductor material and a cathode region of n⁺-conductivesemiconductor material.

The invention is detailed below using the attached drawings onembodiments.

FIG. 1a shows a high voltage diode with punch-through dimensioning asthe first embodiment of the invention;

FIG. 1b shows a diagram of the electrical field in the diode from FIG.1a;

FIG. 2a shows a high voltage diode with non-punch-through dimensioningas the second embodiment of the invention;

FIG. 2b shows a diagram of the electrical field within the diode fromFIG. 2a;

FIG. 3 shows a high voltage diode as the third embodiment of theinvention;

FIG. 4 shows a high voltage diode as the fourth embodiment of theinvention;

FIG. 5 shows a phototriggerable thyristor as the fifth embodiment of theinvention;

FIG. 6 shows a gate turn-off thyristor as the sixth embodiment of theinvention;

FIG. 7 shows a photodiode as the seventh embodiment of the invention.

A high voltage diode as shown in FIG. 1a has a p⁺-conductive anoderegion 1 and a n⁺-conductive cathode region doped n⁻-base region 3 inthe lateral direction x. The lateral length I of the base region 3 isthus greater than the vertical thickness d_(B).

As claimed in the invention, there are compensation layers 6 and 7 onthe outer sides of the base region 3 and they have a charge carrier typewhich is opposite the charge carrier type of the base region, heretherefore p-conductive. The dopant concentration N_(A) in thecompensation layers 6, 7 is chosen here such that it corresponds to thedopant concentration in the base region 3 between the compensationlayers or is somewhat less. FIG. 1b shows the distribution of theelectrical field strength in the diode in which the space charge of then⁻-base and the space charge of the p-conductive compensation layers 6,7 are compensated with corresponding integration over the z direction.The field strength in the anode area 1 thus drops to a value E_(m),remains constant over the lateral length 1 of the base region 3 sincethe surface charge density in the x direction likewise remains constant,and increases again in the cathode region 2 to zero. The entire voltagedrop is formed as the integral of the field strength E over the lateralextension x. Based on the flat distribution of the electrical fieldstrength E over x, the field strength at any time can be less than thebreakdown field strength of the silicon material used and still a largeintegral (area under the curve) can be achieved. This diode can bedimensioned especially in punch-through dimensioning to improve theon-state behavior in which the base width is chosen such that theelectrical field at higher blocking voltages extends into the cathoderegion 2.

FIG. 2 shows a high voltage diode in which in contrast to FIG. 1 thecompensation layers 6 and 7 are changed in the lateral direction x.Thus, sections a, b and c in the lateral direction are made insuccession; for them there are different dopant concentrations in thelayers 7 a, 7 b, 7 c, 6 a, 6 b, 6 c. In the example shown in diagram 2b, in section a, i.e. in the entire volume from 0 to 1 a, the overalldoping of the compensation layers 6 a and 7 a is greater than the dopingof the corresponding section 3 a of the base region so that the fieldstrength in region 3 a continues to drop towards the cathode. In sectionb (between 1 a and 1 b) the overall doping of the compensation layers 6b and 7 b is equal to the doping of the base region 3 b so that thefield strength remains constant here; in section c the overall doping ofthe compensation layers 6 c and 7 c is less than the overall doping ofthe corresponding section 3 c of the base region; optionally in thissection c the compensation layers 6 c and 7 c may not be doped at all.As shown in FIG. 2b, the possible result is thus that the electricalfield strength does not extend into the cathode region 2 so that a highvoltage diode in non-punch through dimensioning results.

Thus it is possible, with maximum field strengths clearly below thebreakdown field strength of the semiconductor material, here silicon, toachieve blocking voltages which are dependent only on the distancebetween the anode and the cathode and thus can be much higher than thevalues which are achieved with conventional components. If for examplewe assume a starting material with doping of 10¹³ cm⁻³ and a thicknessof 200 microns, with a maximum field strength of roughly 60% of thebreakdown field strength at a distance of 3 mm between the anode andcathode, a blocking voltage of 30 kV can be attained.

FIGS. 3 and 4 correspond to FIGS. 1 and 2, here the anode region 1 andthe cathode region 2 not extending over the entire vertical thickness ofthe base region 3. Thus the anode region 1 and the cathode region 2 areeither at the same vertical height as in FIG. 3 or they are verticallyoffset to one another as in FIG. 4.

In the illustrated examples of FIGS. 1 to 4, the anode and cathoderegions directly border the compensation layers 6 and 7, but there canalso be intervals in between. For making contact, an anode terminal 10with an anode contact A is attached to the anode region 1, a cathodeterminal 11 with an cathode contact K is attached to the cathode region2. The lateral length of the base region 3 between the anode region 1and the cathode region 2 is for example 2 mm, the lateral length of theanode region 1 and the cathode region 2 is 0.3 mm each, the verticalwidth of the base region 3 including the compensation layers 6 and 7 isfor example 0.4 mm. Thus, the lateral length of the base region 3 isroughly five times its vertical width. The doping of the base region isfor example 3.5×10¹⁷ cm⁻³. The p-conductive compensation layers can forexample also be formed by ion implantation and with respect to thedopant concentration show concentration variations with a surfaceconcentration of 10¹⁷ cm⁻³ and a penetration depth of 0.31 microns; thiscorresponds to a dopant surface concentration of 7×10¹¹ cm⁻² percompensation layer. At the penetration depth thus the dopant surfaceconcentrations of the base region and the compensation layers correspondand are each 2×7×10¹¹ cm⁻², here the penetration depth can be regardedas the vertical thickness d₆, d₇ of the compensation layers.Furthermore, the compensation layers can also be applied by epitaxy withthe corresponding vertical thickness.

For the phototriggerable thyristor as shown in FIG. 5, between thecathode region 2 and the base region 3 there is additionally ap⁺-conductive fourth region 17 which is partially also in contact withthe cathode terminal 11. Thus the cathode region 2, the fourth region17, the base region 3 and the anode region 1 form a four-layerthyristor, and in one part of the base region 3 via the transparentconnecting region 12 light of a LED 13 can be emitted via its sidesurface 14 which faces the base region. As claimed in the invention, thecompensation regions 6 and 7 extend at least over this part of the baseregion 3 which is exposed to light so that here too at least partialcompensation of the space charges of the base region 3 and thecompensation layers 6 and 7 occurs.

In the gate turn-off transistor as shown in FIG. 6, between then⁺-conductive cathode region 2 and the p-conductive anode region 1 whichis made as an anode emitter, a p-base 5, a n⁻-base 3 and a n⁺-buffer 15are formed. The gate terminal 9 with the gate contact G is likewiseconnected to the p-base 5 via a p⁺-conductive gate region 18. As claimedin the invention, compensation layers 8 are formed from p-conductivesilicon as strips or channels outside and/or inside the n⁻-base 3 in thelateral direction which points up in the drawing. Here the strips extendover the entire thickness of the semiconductor component (y direction),channels are surrounded by the n⁻-base region. Thus higher currents canbe achieved through the base region 3 by forming several layers. Thelateral extension of the compensation structures is for example 2microns, the cell width is 300 microns, large areas can be formed by thearrangement of several cells next to one another.

The compensation layers 8 can extend to the buffer region 15 or,depending on the desired field strength distribution, end before.Production can be done by etching grooves or channels and subsequentdoping, for example by filling with doped polysilicon or by diffusion.FIG. 6 shows an individual structural cell which can be continuedperiodically in the lateral direction in order to achieve for examplecomponent areas from 50 to 70 cm².

The photodiode for producing high voltage pulses as shown in FIG. 7 hasa structure similar to the diode from FIG. 3. The part of the base area3 exposed to external light radiation is thus surrounded accordingly bycompensation layers 6 and 7 so that here complete or partialcompensation of the space charge of the n⁻-conductive base region 3 andthe p-conductive compensation layers 6 and 7 is achieved. Thisphotodiode can accordingly be built up also with the anode region 1 andthe cathode region 2 offset vertically to one another as shown in FIG.4. Injection of light signals can be done via a transparent connectingregion 12 and an optical fiber 16. The component should be dimensionedpreferably such that the electrical field strength in the space chargezone at the prevailing blocking voltage is 60% to 70% of the breakdownfield strength of silicon. Corresponding irradiation results in that inthe irradiated space of the space charge zone a high concentration offree charge carriers is generated. These charge carriers carry a currentwhich flows in the unirradiated regions of the space charge zone as adisplacement current.

The leads to an increase of the field strength in the unilluminatedregion of the space charge zone which ultimately results in strongionization when the breakdown field strength is reached. The diode isthis suddenly flooded with charge carriers and becomes conductive. Thevoltage over the diode collapses almost completely. Since theseprocesses proceed very quickly, on a series-connected load voltage risespeeds of more than 100 kV/microsecond can thus be achieved. As a resultof the remaining voltage on the diode, the generated charge carriersdrain, after this current pulse the diode passes back into its blockingstate.

By illumination of the base region and the diode from FIG. 7 over acorrespondingly large area triggering times in the nanosecond range canbe achieved.

Reference number list 1 anode region 2 cathode region 3 base region 5second base region 6,6a,b,c compensation layer 7,7a,b,c compensationlayer 8 compensation layer 9 gate terminal 10 anode terminal 11 cathodeterminal 12 transparent connecting region 13 LED 14 side surface of theLED 15 buffer region 16 optical fiber 17 fourth region 18 gate region Aanode contact K cathode contact G gate contact a,b,c sections of thesemiconductor component in the lateral direction E electrical fieldstrength x lateral direction Z vertical direction

What is claimed is:
 1. Semiconductor component, especially for highvoltage applications, with low-doped base region (3) of the firstconductivity type (n) extending in the lateral direction (x), twoterminal areas (1, 2) which are separated at least by the base region(3) in the lateral direction (x) for connection to electrical contacts(A, K), characterized in that the base material of the base region (3)is silicon (Si), with a dopant concentration of 10¹² to 5×10¹⁴ cm⁻³, thedopant surface concentration (N_(A)) which has been determined byintegration of the dopant concentration over the vertical thickness ofthe base region (3) along the lateral direction (x) being less than2×10¹² cm⁻², and there are compensation layers (6, 6 a, 6 b, 6 c, 7, 7a, 7 b, 7 c, 8) of the second conductivity type (p) opposite the firstconductivity type which extend inside or outside the base region in thelateral direction (x), the lateral length (l_(K)) of the compensationlayers being greater than their vertical thickness (d₆, d₇) and a dopantsurface concentration (N_(A)) which has been determined by integrationof the dopant concentration over the vertical thickness of acompensation layer along the lateral direction (x) being less than1×10¹² cm⁻².
 2. Semiconductor component as claimed in claim 1, whereinthe lateral length (L) of the base region (3) is greater than thevertical thickness (d) of the base region.
 3. Semiconductor component asclaimed in claim 1, wherein in the first sections (a) along the lateraldirection (x) the dopant surface concentration of the compensationlayers (6 a, 7 a) which has been determined by integration of the dopantconcentration over the vertical thickness is greater than the dopantsurface concentration of the base region (3 a) which has been determinedby integration of the dopant concentration over the vertical thickness.4. Semiconductor component as claimed in claim 1, wherein in the secondsections (b) along the lateral direction (x) the dopant surfaceconcentration of the compensation layers (6 b, 7 b) which has beendetermined by integration of the dopant concentration over the verticalthickness corresponds to the dopant surface concentration of the baseregion (3 b) which has been determined by integration of the dopantconcentration over the vertical thickness.
 5. Semiconductor component asclaimed in claim 1, wherein in the third sections (c) along the lateraldirection (x) the dopant surface concentration of the compensationlayers (6 c, 7 c) which has been determined by integration of the dopantconcentration over the vertical thickness is less than the dopantsurface concentration of the base region (3 c) which has been determinedby integration of the dopant concentration over the vertical thickness.6. Semiconductor component as claimed in claim 3, wherein in the lateraldirection (x) it has several successive sections (a, b, c) withdifferent dopant concentration of the compensation layers (6 a, 6 b, 6c, 7 a, 7 b, 7 c).
 7. Semiconductor component as claimed in claim 1,wherein the base material has a dopant concentration from 4×10¹² to4×10¹⁴, especially 8×10¹² to 10¹⁴ cm⁻³.
 8. Semiconductor component asclaimed in claim 1, wherein the compensation layers (6, 6 a, 6 b, 6 c,7, 7 a, 7 b, 7 c) are formed on the outside surfaces of the base region(3).
 9. Semiconductor component as claimed in claim 1, wherein thecompensation layers (8) are located within the base region andpreferably divide the base region (3) into several component regions.10. Semiconductor component as claimed in claim 1, wherein the anoderegion (1) and/or the cathode region (2) border the compensation layers(6, 7).
 11. Semiconductor component as claimed in claim 10, wherein theanode region (1) and/or the cathode region (2) extend only partiallyover the vertical thickness of the base region (3).
 12. Semiconductorcomponent as claimed in claim 11, wherein the anode region (1) and thecathode region (2) are at the same vertical height.
 13. Semiconductorcomponent as claimed in claim 11, wherein the anode region (1) and thecathode region (2) are arranged vertically offset to one another. 14.Semiconductor component as claimed in claim 10, wherein it is made as adiode, preferably a high voltage diode.
 15. Semiconductor component asclaimed in claim 14, wherein it is made as a photodiode, there beingcompensation layers (6, 7) in the part of the base region (3) which canbe exposed to light radiation.
 16. Semiconductor component as claimed inclaim 10, wherein it is made as a thyristor, between the n⁺-conductivecathode region (2) and the n-conductive base region (3) a p-conductivefourth region (5, 17) being formed.
 17. Semiconductor component asclaimed in claim 16, wherein it its made as a phototriggerablethyristor, the part of the base region (3) which can be exposed to lightradiation having compensation layers (6, 7).
 18. Semiconductor componentas claimed in claim 16, wherein it is made as a thyristor triode, thep-conductive fourth region being made as a second base region (5) andthe gate region (18) of p⁺-conductive semiconductor material forconnection to the gate contact (G) bordering the second base region (5).19. Semiconductor component as claimed in claim 18, wherein an⁺-conductive buffer region is formed between the base region (4) andthe anode region (1).